Disk drive for optimizing write current settings relative to drive operating characteristics and ambient temperature readings

ABSTRACT

A disk drive is disclosed for optimizing write current settings relative to drive operating characteristics and an ambient temperature reading. Test data is written to and read from the disk using different write current settings to generate a plurality of corresponding quality metrics. The quality metrics are evaluated to generate an optimized write current setting for the ambient temperature reading. In one embodiment, the first write current setting is selected relative to a previously optimized write current setting that corresponds to the ambient temperature reading. This embodiment expedites the optimization process by testing write current settings surrounding a previous write current setting rather than testing the entire range of write current settings.

This application is a continuation of co-pending U.S. patent applicationSer. No. 10/136,760 filed on Apr. 30, 2002.

CROSS REFERENCE TO RELATED APPLICATIONS AND PATENTS

This application is related to U.S. Pat. No. 6,369,972 entitled“TEMPERATURE MONITORING METHOD OF A DISK DRIVE VOICE COIL MOTOR FROM ATRAVELED DISTANCE” the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to disk drives for computer systems. Moreparticularly, the present invention relates to a disk drive optimizingwrite current settings relative to drive operating characteristics andambient temperature readings.

2. Description of the Prior Art

The prior art has suggested to compute nominal write current settingsover a plurality of ambient temperatures relative to the coercivity ofthe media used for a plurality of disk drives in a product line.Typically a lower write current is used for higher ambient temperaturesto help minimize inter-track interference, whereas a higher writecurrent is used for lower ambient temperatures to ensure the mediasaturates. During normal “in-the-field” operation, a write drivercircuit is programmed with the appropriate nominal write current settingrelative to the ambient temperature of the disk drive. However,computing nominal write current settings relative to the coercivity ofthe media may not provide the optimal write current settings for eachambient temperature. Further, using static, nominal write currentsettings does not compensate for changes in the drive operatingcharacteristics occurring over time while in-the-field (e.g.,environmental changes and electrical and mechanical changes).

There is, therefore, a need to better optimize the write current in adisk drive relative to drive operating characteristics and the ambienttemperature.

SUMMARY OF THE INVENTION

An embodiment of the present invention comprises a disk drive havingdrive operating characteristics, the disk drive comprising a disk, ahead actuated radially over the disk, and a programmable write driverfor applying a write current to the head during write operations. Awrite current optimization procedure is executed by obtaining an ambienttemperature reading, programming the write driver with a first writecurrent setting relating to the ambient temperature reading, and writingtest data to the disk. The test data is read from the disk and a firstquality metric is generated. The write driver is programmed with asecond write current setting relating to the ambient temperaturereading. The test data is again written to the disk and read from thedisk to generate a second quality metric. The first and second qualitymetrics are evaluated to generate an optimized write current settingbased on the drive operating characteristics and the ambient temperaturereading. The first write current setting is selected relative to apreviously optimized write current setting that corresponds to theambient temperature reading.

Another embodiment of the present invention comprises a method ofexecuting a write current optimization procedure for a disk drive havingdrive operating characteristics. The disk drive comprises a disk, a headactuated radially over the disk, and a programmable write driver forapplying a write current to the head during write operations. An ambienttemperature reading is generated, the write driver is programmed with afirst write current setting relating to the ambient temperature reading,and test data is written to the disk. The test data is read from thedisk and a first quality metric is generated. The write driver isprogrammed with a second write current setting relating to the ambienttemperature reading. The test data is again written to the disk and readfrom the disk to generate a second quality metric. The first and secondquality metrics are evaluated to generate an optimized write currentsetting based on the drive operating characteristics and the ambienttemperature reading. The first write current setting is selectedrelative to a previously optimized write current setting thatcorresponds to the ambient temperature reading.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a disk drive according to an embodiment of the presentinvention comprising a programmable write driver and a disk controllerresponsive to a temperature sensor for optimizing write current settingsfor the write driver.

FIG. 1B shows the steps executed by the disk controller to optimize thewrite current settings according to an embodiment of the presentinvention.

FIG. 2 shows an embodiment of the present invention wherein the writecurrent optimization procedure is executed in a temperature controlledenvironment and the resulting optimized write current settings arere-optimized for a product line of disk drives in a non-temperaturecontrolled environment.

FIG. 3 illustrates that in one embodiment the optimized write currentsettings are adjusted by an offset relative to a write current settingoptimized by each of the product line of disk drives.

FIG. 4 shows a table of write current settings relating to a pluralityof ambient temperature readings for use in programming the write driverduring the write current optimization procedure.

FIG. 5 is a flow diagram illustrating a write current optimizationprocedure executed during an idle mode of the disk drive according to anembodiment of the present invention.

FIG. 6 shows how quality metrics may be generated for optimizing thewrite current settings according to an embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A shows a disk drive 2 according to an embodiment of the presentinvention having drive operating characteristics and comprising a disk 4and a head 8 actuated radially over the disk 4. A programmable writedriver 10 applies a write current to the head 8 during write operations.A disk controller 12 executes a write current optimization procedureshown in FIG. 1B, wherein at step 14 the write driver 10 is programmedwith a first write current setting relating to an ambient temperaturereading. At step 16 test data is written to the disk 4 and read from thedisk 4 to generate a first quality metric. At step 18 the write driver10 is programmed with a second write current setting relating to theambient temperature reading. At step 20 test data is again written tothe disk 4 and read from the disk 4 to generate a second quality metric.At step 22 the first and second quality metrics are evaluated togenerate an optimized write current setting based on the drive operatingcharacteristics and the ambient temperature reading.

In the embodiment shown in FIG. 1A, the disk drive 2 comprises atemperature sensor 24 for obtaining the ambient temperature reading. Inan alternative embodiment, the disk controller 12 executes a temperaturesensing algorithm to obtain the ambient temperature reading. An exampletemperature sensing algorithm may correlate seek distances with ambienttemperature similar to the method disclosed in the above-identifiedpatent application entitled “TEMPERATURE MONITIORING METHOD OF A DISKDRIVE VOICE COIL MOTOR FROM A TRAVELED DISTANCE”.

In one embodiment, the ambient temperature reading is obtained whileexecuting the write current optimization procedure during manufacturing.In an alternative embodiment, the temperature sensor 24 generates theambient temperature reading for the disk drive 2 while executing thewrite current optimization procedure in-the-field. The optimized writecurrent settings are stored in a semiconductor memory. Executing thewrite current optimization procedure in-the-field to re-optimize thewrite current settings compensates for changes in the drive operatingcharacteristics that occur over time due to environmental changes (e.g.,changes in humidity, altitude, etc.) as well as electrical andmechanical changes (e.g., changes in the head resistance, head flyheight, structural resonances, etc.).

In one embodiment, each disk drive individually performs the writecurrent optimization procedure, and in an alternative embodiment, asubset of disk drives within a product line execute the write currentoptimization procedure to generate a plurality of optimized writecurrent settings that are re-optimized for each disk drive in theproduct line. The latter embodiment is illustrated in FIG. 2 wherein adisk drive 26 within a product line executes the write currentoptimization procedure for a plurality of different temperature readingsin a temperature controlled environment to generate a plurality ofoptimized write current settings 28. The optimized write currentsettings 28 are then re-optimized for a plurality of disk drives 30 ₀–30_(N) in the product line.

In one embodiment, each disk drive 30 _(i) in the product line performsthe write current optimization procedure in order to re-optimize thewrite current settings 28 for each individual disk drive 30 _(i). Thatis, the optimized write current settings 28 are treated as defaultsettings which are re-optimized for each disk drive 30 _(i) by executingthe write current optimization procedure for a plurality of differenttemperature readings. In one embodiment, each disk drive 30 _(i) in theproduct line executes the write current optimization procedure during amanufacturing process in a temperature controlled environment, and inalternative embodiment, each disk drive 30 _(i) executes the writecurrent optimization procedure while in-the-field using the currentambient temperature reading for the current drive operatingcharacteristics.

In an alternative embodiment, each disk drive 30 _(i) in the productline executes the write current optimization procedure in anon-temperature controlled environment to generate an optimized writecurrent setting for the current ambient temperature reading. Theoptimized write current settings 28 are then re-optimized for each diskdrive 30 _(i) by adjusting the optimized write current settings 28 by acorresponding offset 34 as illustrated in FIG. 3 which shows thecalibrated write current settings 28 for a plurality of ambienttemperature readings. A disk drive 30 _(i) in the product line executesthe write current optimization procedure for a current ambienttemperature reading to generate a drive specific optimized write currentsetting 32. The optimized write current settings 28 are then adjusted bythe offset 34 to generate a plurality of re-optimized write currentsettings 36 for each disk drive 30 _(i) in the product line. Anadvantage of this embodiment is that while the optimized write currentsettings 28 are generated in a temperature controlled environment atmultiple temperature settings for a small subset of disk drives (evenone), the re-optimized write current settings for each of the diskdrives 30 ₀–30 _(N) in the product line are generated in anon-temperature controlled environment where temperature is relativelyconstant.

The disk 4 in FIG. 1A comprises a plurality of radially spaced,concentric data tracks 6 each comprising a plurality of data sectors andembedded servo sectors 38. The data tracks 6 are banded together to forma plurality of zones (Z1–Z3). The data rate is increased from the innerdiameter zone Z1 to the outer diameter zone Z3 in order to achieve amore constant linear bit density, thereby achieving higher capacity. Inone embodiment, a data sector is reserved in each zone for writing andreading the test data during the write current optimization procedure,and a plurality of write current settings are optimized for each zone.During normal operation the write driver 10 is programmed with theoptimized write current setting corresponding to the current zone andthe current ambient temperature reading.

FIG. 4 shows a table of write current settings for a plurality oftemperature readings TEMP 1-TEMP N wherein the write driver 10 isprogrammed with a plurality of the write current settings relating tothe ambient temperature reading during the write current optimizationprocedure. The write current settings shown in FIG. 4 are notnecessarily stored by the disk drive 2 but may be computed by the diskcontroller 12. For example, the disk controller 12 may select a startingwrite current setting (e.g., the current optimized write currentsetting) and then generate a plurality of write current settings byincrementing/decrementing the starting write current setting by apredetermined delta (e.g., one milliamp). In this manner the writedriver 10 is programmed over a range of write current settings relativeto the starting write current setting.

In one embodiment, during the write current optimization procedure aquality metric is generated for each of the possible write currentsettings relating to the ambient temperature reading. In anotherembodiment, a quality metric is generated over a subset of the writecurrent settings proximate the current optimized write current setting.For example, in FIG. 4 if the ambient temperature reading corresponds toTEMP 1, the optimization procedure may generate a quality metric for asubset of write current settings proximate to the current optimizedwrite current setting Ti1-3 (e.g., write current settings Ti1-1 toTi1-5). This embodiment may be more efficient, particularly if thenumber of possible write current settings is very large. In oneembodiment, the optimization procedure is periodically executed over theentire set of possible write current settings for a given ambienttemperature reading to ensure the optimal setting does not fall outsidethe subset surrounding the current optimized setting.

FIG. 5 is a flow diagram illustrating an embodiment of the presentinvention wherein the write current optimization procedure is executedby the disk drive in-the-field during an idle mode to compensate forchanges in the drive operating characteristics that occur over time(e.g., environmental changes or electrical and mechanical changes). Ifat step 40 the disk drive is in an idle mode, then at step 42 a currenttemperature reading is taken from the temperature sensor 24. If at step43 the write current setting for the current temperature reading hadbeen previously optimized within a predetermined time interval, theoptimization procedure exits. Otherwise at step 44 the write driver 10is programmed with a write current setting relating to the temperaturereading (see FIG. 4). At step 46 test data is written to and read fromthe disk to generate a quality metric, and at step 48 the quality metriccorresponding to the write current setting is stored. If at step 50there are more write current settings to try, the processes repeatsstarting with step 44. After generating a quality metric for each of thewrite current settings, at step 52 the quality metrics are evaluated andat step 54 the optimal write current setting relative to the qualitymetrics is selected as the re-optimized write current setting usedduring normal operation. The re-optimized write current setting may beone of the write current settings programmed into the write driver 10 atstep 44, or it may be computed for example by interpolating betweenwrite current settings programmed into the write driver 10 at step 44.

The quality metrics used to select the operating write current settingmay be generated in any suitable manner. FIG. 6 shows two examples ofhow quality metrics can be generated within a disk drive employing asampled amplitude read channel. The read signal 56 emanating from thehead 8 is sampled by a sampling device 58 to generate read signal samplevalues 60. The read signal sample values 60 are processed by a timingrecovery circuit 62 in order to synchronize the sampling to a zone datarate. The timing recovery 62 may be implemented in any suitable manner,such as adjusting the sampling frequency of the sampling device 58, orby interpolating the read signal sample values 60. The read signalsample values 60 are equalized by an equalizing filter 64 according to adesired response corresponding to a desired detection algorithm (e.g.,partial response maximum likelihood (PRML)). A difference between theequalized read signal sample values 66 and expected sample values 68 iscomputed to generate a difference value 70. The difference or error issquared 72, and the squared values 74 summed 76 to generate the qualitymetric 78. In on embodiment, the write current setting which generatesthe minimum quality metric (e.g., the least mean squared (LMS) error) isselected as the re-optimized write current setting used during normaloperation. In the embodiment shown in FIG. 6, the expected sample values68 are generated by an expected sample value generator 80 in response tothe test data 82 generated by a test data generator 84 (which generatesthe test data 82 written to and read from the disk 4 during thecalibration procedure). Techniques for generating expected sample values68 from a test data sequence are known and not disclosed so as not toobscure the embodiments of the present invention.

The equalized sample values 66 in FIG. 6 are processed by a sequencedetector 86 (e.g., a Viterbi detector) to generate an estimated datasequence 88. In one embodiment, the estimated data sequence 88 iscompared to the test data 82 (e.g., using an XOR circuit 90) to generatebit errors 92. The bit errors are accumulated (counted) by summingcircuit 94 to generate a quality metric 96. In one embodiment, the writecurrent setting which generates the minimum quality metric (the leastnumber of bit errors) is selected as the re-optimized write currentsetting used during normal operation. In another embodiment, the qualitymetric 96 representing the number of bit errors is generated by an errordetection and correction algorithm 98, such as the well knownReed-Solomon error correction code (ECC). In one embodiment, multiplequality metrics (e.g., both quality metrics 78 and 96 in FIG. 6) aregenerated and evaluated to select the re-optimized write current settingused during normal operation.

The aspects of the present invention, including the calibrationprocedure and quality metrics, may be implemented in circuitry, softwareor a combination of circuitry and software. The disk controller 12 andother circuitry may be implemented in a plurality of integrated circuitsor a single integrated circuit. In one embodiment, the temperaturesensor 24 is enclosed in a head disk assembly (HDA) for housing the disk4, head 8, a voice coil motor (VCM) for actuating the head 8, and apreamp circuit (not shown). Any suitable temperature sensor 24 may beemployed in the embodiments of the present invention.

In one embodiment, the write current optimization procedure is executedas part of a write-verify procedure which verifies the recoverability ofa data sector after being written to the disk. If the write-verifyprocedure fails, the disk drive may execute the write currentoptimization procedure and then re-write the data sector to the diskusing the re-optimized write current setting. In yet another embodiment,the write current optimization procedure is executed as part of a heroicerror recovery procedure wherein a data sector unrecoverable on-the-flyusing error correction code (ECC) circuitry is recovered using variousfirmware error recovery procedures (e.g., introducing a tracking offsetinto the servo system). After recovering a marginal data sector usingthe heroic error recovery procedures, the disk drive may execute thewrite current optimization procedure and then re-write the errant datasector using the re-optimized write current setting.

Periodically calibrating the write current settings compensates forchanges in the drive operating characteristics that occur over time(e.g., environmental changes or electrical and mechanical changes). Ineffect, the optimized write current settings adapt to the dynamics ofthe drive operating characteristics which overcomes the problemsassociated with the static write current settings that are employed inthe prior art.

1. A disk drive having drive operating characteristics, the disk drivecomprising: (a) a disk; (b) a head actuated radially over the disk; (c)a programmable write driver for applying a write current to the headduring write operations; (d) a disk controller for executing a writecurrent optimization procedure by: obtaining an ambient temperaturereading; programming the write driver with a first write current settingrelating to the ambient temperature reading; writing test data to thedisk; reading the test data from the disk and generating a first qualitymetric; programming the write driver with a second write current settingrelating to the ambient temperature reading; writing test data to thedisk; reading the test data from the disk and generating a secondquality metric; and evaluating the first and second quality metrics togenerate an optimized write current setting based on the drive operatingcharacteristics and the ambient temperature reading, wherein the diskcontroller selects the first write current setting relative to apreviously optimized write current setting that corresponds to theambient temperature reading.
 2. The disk drive as recited in claim 1,wherein the disk drive further comprises a temperature sensor to obtainthe ambient temperature reading.
 3. The disk drive as recited in claim1, wherein the disk controller executes a temperature sensing algorithmto obtain the ambient temperature reading.
 4. The disk drive as recitedin claim 1, wherein the disk controller executes the write currentoptimization procedure during a manufacturing process.
 5. The disk driveas recited in claim 1, wherein the disk controller executes the writecurrent optimization procedure for a plurality of different ambienttemperature readings to generate a plurality of corresponding optimizedwrite current settings.
 6. The disk drive as recited in claim 1,wherein: (a) the disk drive comprises a semiconductor memory for storingoptimized write current settings; (b) the disk controller executes thewrite current optimization procedure in-the-field based on the driveoperating characteristics at the time the write current optimizationprocedure is executed; and (c) the optimized write current settinggenerated by the write current optimization procedure is used tore-optimize at least one of the optimized write current settings storedin the semiconductor memory.
 7. The disk drive as recited in claim 1,wherein the disk controller executes the write current optimizationprocedure during an idle mode of the disk drive.
 8. The disk drive asrecited in claim 1, wherein: (a) the head generates a read signal whilereading the test data from the disk; (b) the disk drive comprises asampling device for sampling the read signal to generate read signalsample values; and (c) the quality metrics comprise a mean squared errormeasurement generated relative to the read signal sample values andexpected sample values.
 9. The disk drive as recited in claim 1, whereinthe quality metrics comprise bit errors in an estimated data sequencedetected from a read signal emanating from the head while reading thetest data from the disk.
 10. A method of executing a write currentoptimization procedure for a disk drive having drive operatingcharacteristics, the disk drive comprising a disk, a head actuatedradially over the disk, and a programmable write driver for applying awrite current to the head during write operations, the method comprisingthe steps of: (a) generating an ambient temperature reading; (b)programming the write driver with a first write current setting relatingto the ambient temperature reading, wherein the first write currentsetting is selected relative to a previously optimized write currentsetting that corresponds to the ambient temperature reading; (c) writingtest data to the disk; (d) reading the test data from the disk andgenerating a first quality metric; (e) programming the write driver witha second write current setting relating to the ambient temperaturereading; (f) writing test data to the disk; (g) reading the test datafrom the disk and generating a second quality metric; and (h) evaluatingthe first and second quality metrics to generate an optimized writecurrent setting based on the drive operating characteristics and theambient temperature reading.
 11. The method as recited in claim 10,wherein the disk drive further comprises a temperature sensor forgenerating the ambient temperature reading.
 12. The method as recited inclaim 10, further comprising the step of executing a temperature sensingalgorithm to generate the ambient temperature reading.
 13. The method asrecited in claim 10, wherein the write current optimization procedure isexecuted during a manufacturing process.
 14. The method as recited inclaim 10, wherein the write current optimization procedure is executedfor a plurality of different ambient temperature readings to generate aplurality of corresponding optimized write current settings.
 15. Themethod as recited in claim 10, wherein the disk drive further comprisesa semiconductor memory, further comprising the steps of: (a) storingoptimized write current settings for the disk drive in the semiconductormemory; (b) executing the write current optimization procedurein-the-field based on the drive operating characteristics at the timethe write current optimization procedure is executed; and (c)re-optimizing at least one of the optimized write current settingsstored in the semiconductor memory in response to the optimized writecurrent setting generated by the write current optimization procedure.16. The method as recited in claim 10, further comprising the step ofexecuting the write current optimization procedure during an idle modeof the disk drive.
 17. The method as recited in claim 10, wherein thehead generates a read signal while reading the test data from the disk,further comprising the steps of: (a) sampling the read signal togenerate read signal sample values; (b) computing a difference between aread signal sample value and an expected sample value to generate adifference value; (c) computing the square of the difference value togenerate a squared value; and (d) summing the squared values to generatethe quality metrics.
 18. The method as recited in claim 10, wherein thehead generates a read signal while reading the test data from the disk,further comprising the steps of: (a) detecting an estimated datasequence from the read signal while reading the test data from the disk;(b) comparing the estimated data sequence with the test data to generatebit errors; and (c) counting the number of bit errors to generate thequality metrics.